The joint of a robot contains a drive mechanism for relatively rotating two coupled members which are to be coupled to each other via the joint. To prevent a lubricant from leaking out of the drive mechanism to an external environment of the robot, or inhibit the entry of foreign matters from the external environment into the joint, seal members are provided in a gap formed between the two coupled members (e.g., see Patent Literature 1).
In the example disclosed in Patent Literature 1, one joint is provided with the two seal members separately. The two coupled members are coupled to each other in such a manner that their peripheral walls are arranged in a rotational axis direction with a small gap between the peripheral walls. The second seal member at an outer side seals the gap formed between the peripheral walls. The second seal member defines the peripheral wall of the whole joint, together with the two coupled members, and is exposed to the external environment.